Progressive fibrosis of the liver, kidney, lungs and other organs frequently results in organ failure that leads to organ transplantation or death, affecting millions in the United States and worldwide. Hepatic fibrosis, for example, is the leading non-malignant gastrointestinal cause of death in the United States, and the progression of fibrosis is the single most important determinant of morbidity and mortality in patients with chronic liver disease. Furthermore, the process of fibrosis is common to liver diseases of many etiologies, including chronic viral hepatitis B and C, autoimmune liver disease such as autoimmune hepatitis, alcoholic liver disease, fatty liver disease; primary biliary cirrhosis; and drug-induced liver disease. The fibrosis seen in these disorders results from chronic insults to the liver such as viral infection, alcohol or drugs.
Hepatitis C, for example, is one of the leading causes of chronic liver disease in the United States, where an estimated 3.9 million people are chronically infected with hepatitis C virus (HCV) and approximately 30,000 new cases of acute HCV occur each year (Alter, Semin. Liver Dis. 15:5-14 (1995)). The prevalence of hepatitis C is estimated to be 1.8% in the United States, with up to 10,000 deaths per year likely resulting from chronic hepatitis C infection (Alter, supra, 1995).
While hepatic fibrosis is a reversible process resulting in the accumulation of extracellular matrix, liver cirrhosis is an irreversible process characterized by thick bands of matrix which completely encircle the parenchyma to form nodules. Untreated, fibrosis of the liver leads to cirrhosis and eventually end-stage liver disease or cancer. Cirrhosis of the liver is a common condition that frequently goes undetected. For example, in a large sample of the general Danish population, the prevalence of liver cirrhosis was 4.5%, of which one-third were undiagnosed at the time of death (Graudal, J. Intern. Med. 230:165-171 (1991)).
Timely and accurate diagnosis of liver fibrosis is important to effective medical treatment. As an example, patients with hepatitis C and cirrhosis are less likely to respond to treatment with α-interferon compared to patients with less advanced disease (Davis, Hepatology 26(Supp. 1):122-127S). Similarly, treatments for chronic HCV infection can be contra-indicated in patients with histologically advanced and decompensated disease (NIH Consensus Development Conference Panel Statement, Hepatology 26 (Suppl. 1):25-105S (1997)). The importance of early diagnosis is further emphasized by the serious early complications such as variceal rupture that are associated with cirrhosis; these complications can be prevented by early detection of cirrhosis (Cals and Pasqual, Gastroenterol. Clin. Biol. 12:245-254 (1988)).
Diagnosis of the presence or severity of fibrotic liver disease is difficult, with liver biopsy currently the most reliable method available. Unfortunately, liver biopsy has several limitations: pain in about 30% of patients; the risk of severe complications such as hemorrhage or infection; a death rate of 3 in 10,000; and the cost of hospitalization (Nord, Gastrointest. Endosc. 28:102-104 (1982); Cadranel et al., Hepatology 32:47-481 (2000); and Poynard et al., Can. J. Gastroenterol. 14:543-548 (2000)). Furthermore, slowly progressive diseases such as hepatitis C require repeated biopsies for continual assessment of disease progression, thus compounding the risks and costs of the procedure. Finally, biopsy can fail to detect disease because of the heterogeneous distribution of pathological changes in the liver; it is not surprising, then, that false negatives are seen in a significant percentage of cases biopsied (Nord, supra, 1982).
For years there has been a search for biochemical or serological markers which reflect fibrotic processes in liver disease and which can serve as a surrogate for liver biopsy. Serological markers for other fibrotic diseases are also of tremendous clinical value. However, the performance of any single marker has not been good enough to substitute for the biopsy procedure in detecting or staging fibrosis. Thus, there is a need for a non-invasive method of diagnosing the presence or severity of liver fibrosis, and other tissue fibrosis. The present invention satisfies this need by providing a convenient and reliable method for detection of liver fibrosis and other tissue fibrosis that is suitable for serial testing. Related advantages are provided as well.